1. Field of the invention
This invention generally relates to a control apparatus based on modern control theory. This invention specifically relates to an automotive control apparatus such as an automotive engine idle speed control apparatus.
2. Description of the Prior Art
Some known control apparatus and methods use modern control theory to improve response characteristics. For example, Japanese published unexamined patent application No. 59-7752 discloses a method of controlling idle speed of an internal combustion engine according to modern control theory. These known control apparatus and methods generally have problems as follows.
(1) In modern control theory, desired control quantity or quanties are calculated on the basis of state variables representing the internal state of a system controlling an controlled object. The state variables are estimated by constructing an observer. Generally, the state variables and the desired control quantity are periodically updated. Specifically, new state variables are estimated from currently detected values outputted by sensors, a preceding control quantity, and preceding state variables according to the observer. A new control quantity is determined on the basis of these new state variables. The object is controlled in accordance with the periodically updated control quantity. The accuracy of construction of an oberver greatly affects the accuracy of the control, so that an accurate observer is necessary for reliable control.
(2) An observer is generally designed through simulation requiring a long time and much labor.
(3) An observer is constructed in correspondence with a model, so that an accurate observer requires accurate modeling which causes a complicated model. The complicated model generally requires lengthy or difficult calculation during the control.